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Guru
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Amplifying 100ps Risetime / Falltime Signal

09/16/2016 11:20 PM

Hello,

I have a problem of Amplifying 100ps risetime / falltime signal of width 5ns to 10ns 0V to about -10mV signal into 50 ohms resistor.

If I use BJT amplifier then either rise time or fall time any one edge becomes fast and other one goes slow due to RC timing. How to manage both edges for fast transitions.

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Guru

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#1

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 12:04 AM

Maybe use two switches...one n o , one n c..

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Guru
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#2
In reply to #1

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 2:46 AM

Hi SolarEagle:

I wonder if it is all that simple.

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#3
In reply to #2

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 4:31 AM
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Guru
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#4
In reply to #3

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 6:25 AM

Yes, they are very fast analog comparators. I need to amplify the signal first.

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#6
In reply to #4

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 1:42 PM

What about a transimpedance amplifier...?

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#5

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 1:07 PM

Is there a specific requirement to preserve the pulse shape, or do you just need to measure the width (or e.g. height)?

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Guru
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#9
In reply to #5

Re: Amplifying 100ps risetime / falltime signal

09/17/2016 11:46 PM

Hi JohnDG:

There is sure need to preserve in incoming first edge which in falling edge due to negative pulse.

There is another need to keep the second edge short such that many more such pulses can be accommodated due to high repeat rate of such pulses. However, it is not RF requirement so only random impulses of events are of concern. I think pulse count rate may not exceed 1 Million/s but they may be randomly close enough with pulse pair resolution down to 10 ns.

Most important is the first part.

I am trying to use BFR92 / BFR93 / BF92 / BFT93 5GHz transistor or 11GHz NXP transistor of low noise and high gain.

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Guru

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#7

Re: Amplifying 100ps Risetime / Falltime Signal

09/17/2016 5:42 PM

How much gain are you wanting? What is the slew rate, as your amplified signal peak edge rate of 100ps needs to have a maximum voltage swing to determine the minimum amplifier slew rate at the gain you are wanting.

Look at "high speed Norton amplifiers".

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#11
In reply to #7

Re: Amplifying 100ps Risetime / Falltime Signal

09/18/2016 2:19 AM

Hi ignator:

The first edge of the negative pulse can be made to slow down to 500ps or <1ns from original 100ps originating from CEM or channel electron multiplier. It also flattens due to cable capacitance. of about 10pF -25pF and load 50 ohms.

The decay portion is larger due to high bias resistance of about 100K to 1M Ohms.

I am not sure if "high speed Norton amplifiers" exist for 400MHz to 900MHz range. Old NS amplifiers were for 10MHz.

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#14
In reply to #7

Re: Amplifying 100ps Risetime / Falltime Signal

09/18/2016 9:28 PM

Signal gain of X100 non-inverting with rise time and fall time 1ns. For -50mV pulse signal the output will be -5V with 5V/ns edges.

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#15
In reply to #14

Re: Amplifying 100ps Risetime / Falltime Signal

09/19/2016 10:50 PM

That's the problem; that amplifier has >about< a 350MHz bandwidth. See http://www.tek.com/support/faqs/how-bandwidth-related-rise-time-oscilloscopes and
http://www.edn.com/electronics-blogs/all-aboard-/4424573/Rule-of-Thumb--1--The-bandwidth-of-a-signal-from-its-rise-time.

The 0.35 factor comes from analog days; using that [0.35/.1(nS)] you'll need at least a 3.5 GHz BW amplifier. Do note the Tektronix mention of .45 as the factor for digital oscilloscopes.

Cortland Richmond

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#16
In reply to #15

Re: Amplifying 100ps Risetime / Falltime Signal

09/20/2016 12:56 AM

Perhaps I can slow down the edge to 1ns to make the frequency range to 1/(3*1ns) = 333MHz. BFR92 and BFT92 transistors are often used for such amplifiers and they are 5GHz, but are getting obsolete. Perhaps I can use

http://www.nxp.com/documents/data_sheet/BFU530XR.pdf

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#17
In reply to #16

Re: Amplifying 100ps Risetime / Falltime Signal

09/20/2016 6:58 AM

Of course that's your decision.

Do you actually require a 100 ps transition time?

Does it have to drive a 50 ohm load?

Do you actually HAVE a 50 ohm, non-reactive load?

You did mention R-C problems; whatever preamplifier you use must be able to charge and discharge the capacitance of your device during the transition time used, and it's possible the devices you tried weren't able to do that. You may find yourself using a preamplifier with somewhat more output power just to pump current in and out of a capacitive load.

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Guru
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#19
In reply to #17

Re: Amplifying 100ps Risetime / Falltime Signal

09/20/2016 9:50 AM

100ps rise time is that of the actual signal from MCP / CEM.

RG58/U is often used to connect which has 50 ohms impedance. Sometime RG59/U can be used with 75 ohms. Problem is that BNC connectors look alike so we avoid a mixed up. Sometime even 91/93 ohms low capacitance cable is preferred but rare to get such connectors. RG58/U 50 ohms 1ft cable has 25pF capacitance and 50 ohms resistance termination changes shape.

Perhaps Capacitance || Resistance can reduce shape alteration but matching for frequencies is again a problem.

Output signal goes to other 50 Ohms terminated signal analyzers such as CFD, TAC trigger sources.

The signal has 1pC charge in 1ns PW of signal of 100ps rise time and signal itself drives the cable up to preamplifier. This is what I have as input signal.

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#8

Re: Amplifying 100ps Risetime / Falltime Signal

09/17/2016 6:29 PM

You need a 50Ω wideband RF / microwave amplifier, and I suggest, NOT a comparator or other nonlinear device. A 10MHz to 2GHz bandwidth should be more than sufficient. This is a commodity area, and there are plenty of choices available. I like larger packages, for soldering ease, and the SC-70 (sot-343) is as small as I like to go.

In a recent project I chose the Avago Broadcom ADA-4543. It has a 4-pin package with two grounds and 50Ω input and out impedances, and its bandwidth is DC to 2.5GHz. It runs on 3.3 to 5.0V and takes 15mA at 3.4V. It costs well under a buck.

You are required to some up with an RF supply inductor.

For wide bandwidth I suggest several inductors in series, with staggered inductance values, the larger one close to the supply and the smallest at the amplifier's output pin. This is to deal with the inductor's self capacitance and impedance; you want the SRF, or self-resonant frequency to be higher than your highest bandwidth for the smaller part, and the inductive impedance to be higher than 50Ω at your lowest frequency for the larger part.

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Guru
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#12
In reply to #8

Re: Amplifying 100ps Risetime / Falltime Signal

09/18/2016 2:26 AM

Hi Winfield Hill:

My target gain is 40dB or voltage gain of 100. Noise figure < 0.5dB. I thought of Mini Circuits.

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#21
In reply to #8

Re: Amplifying 100ps Risetime / Falltime Signal

10/03/2016 1:35 AM

HI Winfield Hill:

I think RFC is good for fixed frequency type amplifier to get peaking voltage amplification and it will also have negative voltage swing from stored energy. Perhaps 10 MHz to 500 MHz flat response voltage amplifier is most suitable for my signal amplification to preserve shape in this frequency range. I need to avoid inductors.

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#10

Re: Amplifying 100ps Risetime / Falltime Signal

09/18/2016 2:00 AM

To preserve the fidelity of a waveform requires a bandwidth of at least 1/t Hz for the fastest transition.

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Guru
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#13
In reply to #10

Re: Amplifying 100ps Risetime / Falltime Signal

09/18/2016 3:20 AM

Yes.

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#18

Re: Amplifying 100ps Risetime / Falltime Signal

09/20/2016 7:51 AM

Am I right in thinking that this is for amplifying some kind of detector output prior to PHA/counting?

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#20
In reply to #18

Re: Amplifying 100ps Risetime / Falltime Signal

09/20/2016 9:53 AM

Yes, indeed it is the CEM / MCP detector (night vision detector if you know are similar) signal which is used for timing or time of flight or time of arrival measurement. Hence, time is the information irrespective of pulse height which is not much information other than separating it from base noise level.

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